1. Field of the Invention
This invention relates generally to a wafer-level package for an integrated circuit that includes a hydrogen getter and, more particularly, to a wafer-level package for one or more integrated circuits that includes an integrated hydrogen getter within and around the integrated circuits.
2. Discussion of the Related Art
It is known in the art to provide wafer-level packages for integrated circuits, such as monolithic millimeter-wave integrated circuits (MMIC), formed on a substrate or cover wafer. In one wafer-level packaging design, a cover wafer is mounted to the substrate wafer using a bonding ring so as to provide a hermetically sealed cavity in which the integrated circuits are provided. Typically, many integrated circuits are formed on the substrate or the cover wafer, where one or more integrated circuits are surrounded by a separate bonding ring. The cover wafer(s) and substrate wafer are then diced between the bonding rings to separate the packages for each separate or combined integrated circuit.
Some of the materials used in fabricating semiconductor integrated circuit devices in wafer-level packages are degraded by hydrogen. For example, certain metal films, such as titanium and platinum, used in the fabrication of integrated circuits react with hydrogen and degrade overtime, eventually rendering the device inoperative. Hydrogen degradation is particularly a problem for high electron mobility transistors (HEMT) that may be included in monolithic millimeter-wave integrated circuits because these devices may have thin nitride passivation layers, allowing hydrogen to penetrate through the thin passivation and degrade the protected metal films underneath.
Hydrogen is able to collect within the hermetically sealed package because hydrogen atoms are very small, and they are slowly able to penetrate into the package from the outside.
In order to alleviate hydrogen degradation of integrated circuit components within wafer-level packages, it has been proposed in the art to provide hydrogen getters within the wafer-level package that absorb the hydrogen to remove it from the sealed cavity. Particularly, it is known in the art to deposit certain layers of material within the wafer-level package that operate to absorb hydrogen that may otherwise degrade some of the semiconductor materials.
FIG. 1 is a cross-sectional view of a wafer-level package 10 including a semiconductor substrate wafer 12 on which one or more integrated circuits 14 have been fabricated by well known processes. A bonding ring 16 is formed on the semiconductor substrate wafer 12, and is bonded to a bonding ring on a cover wafer 20 so as to provide a hermetically sealed cavity 22 in which the integrated circuits 14 are provided. Signal lines and ground lines (not shown) would be provided within the package 10 to the outside, either through the substrate wafer 12 or the cover wafer 20 using vias, or laterally through the bonding ring 16, to make electrical connections to the integrated circuits 14. It has been proposed in the art to deposit a hydrogen getter 30 on an under-side of the cover wafer 20 within the cavity 22 that acts to absorb hydrogen within the cavity 22. In practice, the hydrogen getter may be deposited on other surfaces within the wafer level package.
FIG. 2 is a cross-sectional view of a portion of the hydrogen getter 30 deposited on the cover wafer 20 including a plurality of hydrogen getter layers. Particularly, the hydrogen getter 30 includes a plurality of metal layers deposited on either the substrate wafer 12 or the cover wafer 20, including but limited to, in no particular order, titanium layers 32, 36 and 40, nickel layers 34 and 38, and a palladium layer 42. The order and thickness of these layers may be varied and adjusted according to the need.